1. Field of the Invention
This invention relates to water-based hydraulic fluids and metalworking compositions.
2. Prior Art
In the technology of hydraulic power transmission, mechanical power is imparted to a fluid called "a hydraulic fluid" in the form of pressure by means of a hydraulic pump. Power is utilized where desired by tapping a source of said hydraulic fluid thus transforming the power as pressure back to mechanical motion by a mechanism called a hydraulic motor. The hydraulic fluid is utilized as a pressure and volume transmitting medium. Any non-compressible fluid can perform this function. Water is the oldest fluid used for this purpose and is still sometimes used alone for this purpose. In the prior art, there has been a heavy emphasis on the development of petroleum oils for use as hydraulic fluids and, consequently, much of the equipment utilized with hydraulic fluids has been designed and manufactured specifically for use with petroleum oils. A petroleum oil in comparison with water as a hydraulic fluid possesses the advantage of inhibiting the development of rust of the ferrous components of the mechanical equipment utilized in conjunction with hydraulic fluids, (i.e., hydraulic pumps, motors, etc.) and in preventing wear of the machinery since the hydraulic fluid must lubricate the equipment. Petroleum oils have a second advantage over the use of water as a hydraulic fluid in that the petroleum oils normally exhibit a substantially higher viscosity than water and thus contribute to reduction of the leakage of the fluid in the mechanical equipment utilized. In addition, the technology relating to additives for petroleum oils has developed to such an extent that the viscosity, foam stability, wear prevention and corrosion prevention properties of such petroleum oil-based hydraulic fluids can be further enhanced by the use of said additives.
Over the past 25 years, various substitutes for petroleum oil-based hydraulic fluids have been developed in order to overcome one of the major deficiencies of petroleum oils, namely, flammability. Recent interest in the use of hydraulic fluids having up to 99 percent or more of water has resulted from the higher cost of petroleum oils and recent emphasis on problems of ecologically suitable disposal of contaminated or spent petroleum oil-based hydraulic fluids.
Metalworking fluids of the so-called "soluble oil" type have been considered for use as hydraulic fluids. Such fluids contain mineral oil and emulsifiers as well as various additives to increase corrosion resistance and improve antiwear and defoaming properties. Such fluids, when used as hydraulic fluids, are not generally suitable for use in ordinary industrial equipment designed specifically for use with the petroleum oil-based hydraulic fluids since such fluids do not adequately prevent wear damage in pumps and valves of such equipment. However, such fluids have found application in specially designed, high cost, large size equipment which, because of said large size and thus inflexibility, is not suitable for use in most industrial plants. The soluble oil hydraulic fluid usage has thus been quite limited; usage has been largely confined to large installations where flexibility and size are not critical, such as in steel mills.
It is known from U.S. Pat. No. 3,249,538 to prepare an aqueous lubricant concentrate and lubricating composition consisting essentially of molybdenum disulfide and a water-soluble viscosity increasing agent such as polyvinyl alcohol and an emulsifiable mineral oil. It is also known from U.S. Pat. No. 3,970,569 to prepare aqueous lubricating compositions containing a water-soluble mixed ester obtained by transesterification of a polyoxyethylene glycol and a triglyceride.
It is also known from U.S. Pat. No. 3,933,658 that a mixture of a phosphate ester and a sulfur compound can be used in a water-based metalworking composition to obtain extreme pressure, antiwear and corrosion inhibiting properties. Such additives are used with a suitable vehicle such as mineral oil, vegetable oil, aliphatic acid ester, etc. The sulfur compounds disclosed are not sulfurized molybdenum compounds but rather are derivatives of 2-mercaptobenzothiazole. The phosphate esters and salts of the instant invention, however, are similar to those disclosed in this reference. These are alkylene oxide derivatives of an alkyl, aryl or aralalkyl phosphate which are converted in situ from the free acid form to the neutralized form wherein the phosphate ester is neutralized with an alkali or alkaline earth metal hydroxide or carbonate, ammonia or an amine. The use of these phosphate ester acids and the sodium or triethanolamine salts thereof in water-based metalworking fluids is suggested in ASLE Transactions 7, pages 398 to 405, at page 405.
It is also known to use, in equipment designed for use in mineral oil-based hydraulic fluids, flame-resistant glycol-water based hydraulic fluids such as are disclosed in U.S. Pat. No. 2,947,699. Up until now, water-based hydraulic fluids containing about 70 to 95 percent water, have had very poor lubricating characteristics. While hydraulic fluids are used primarily to transmit forces, it is necessary that they provide lubrication for the impeller, rings, vanes, gears, pistons and cylinders and other mechanical parts of hydraulic pumps in such systems in order to prevent excessive wear on such parts.
Many prior art fluids, such as the petroleum oil type, are highly flammable and unsuitable for certain uses where such fluids have frequently been the source of fire. Where these fluids are used to control such industrial operations as heavy casting machines, which are operated largely by hydraulic means, danger of fire exists. Therefore, there is a growing demand for hydraulic fluids characterized by reduced flammability.
Hydraulic fluids obtained by blending water and a synergistic mixture of a phosphate ester, with a sulfur-containing compound, etc., and where desirable, a polyglycol type polymeric thickener to increase viscosity are disclosed in U.S. Pat. No. 4,138,346. The sulfur compounds employed in the patent are ammonia, amine or metal salts of 2-mercaptobenzothiazole or 5-, 6-, or 7-substituted 2-mercaptobenzothiazole.
Molybdenum oxide phosphorodithioates are disclosed in U.S. Pat. No. 3,402,188 as useful as additives in power transmitting fluids. It appears that the power transmitting fluids with which these compounds may be used are those which are soluble in hydrocarbon compositions in view of the statement at the beginning of the patent:
"Those which are soluble in hydrocarbon compositions have found uses as additives in gasolines, fuel oils, lubricating oils and greases, cutting oils, transformer oils, hydraulic fluids, and other power transmitting fluids."
A hydraulic fluid or metalworking lubricant, of compositions having water as a base and yet possessing superior lubricating and wear preventing characteristics, is disclosed in U.S. Pat. No. 4,151,099. The fluids comprise (1) a water-soluble polyoxyethylated ester of an aliphatic acid and a monohydric or polyhydric aliphatic alcohol, either one or both said acid and said alcohol being polyoxyethylated, (2) a sulfurized molybdenum or antimony compound or alternatively mixtures of (1) and (2) with (3) a phosphate ester salt. In accordance with this patent, the water-soluble polyoxyethylated ester (1) is an essential component while the phosphate ester salt (3) may be employed but is not essential.
In no one of the references discussed above is there any suggestion that a water-based hydraulic fluid or metalworking lubricant can be provided by combining (1) a sulfurized molybdenum or antimony compound with (2) a phosphate ester or salt thereof.